Discharge control for hydraulic classification



Oct. 25, 1966 R. D. EVANS 3,280,975

DISCHARGE CONTROL FOR HYDRAULIC CLASSIFICATION Filed March 29, 1963 1.:INVENTOR.

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Af/amey United States Patent 3,280,975 DISCHARGE CONTROL FOR HYDRAULICCLASSIFICATION Robert D. Evans, Pierce, Fla, assignor, by mesneassignments, to Continental Oil Company, a corporation of Delaware FiledMar. 29, 1963, Ser. No. 268,899 9 Claims. (Cl. 209-158) This inventionrelate-s to the hydraulic classification of particulate solids, andespecially to methods and instrument-aities for effecting productdischarge from a s-o-called hindered settling column wherein dividedsolid material is classified according to settling rate.

In hydraulic classifiers of the type including a hindered settlingcolumn, for classifying solid materials by particle size or settlingrate, an eifective mode of withdrawal of accumulating, classifiedmaterial from the column involves a siphon under control of a so-calledhydrostatic column, i.e. as embraced in US. Patent No. 2,714,958 grantedAugust 9, 1955 on an application of the present applicant. Essentialfeatures of an advantageous embodiment of the siphon discharge of thepatent include siphon conduit means extending above the uppermost levelof liquid in the classifier, arranged to discharge at an externallocality below said level, together with a control device including ahydrostatic pipe opening in the classifier at a level adjacent the inletopening of the siphon and extendin-g well above the classifier. Thehydrostatic pipe comm-unicates with a control chamber at a selectedelevation i.e. above the uppermost portion of the siphon, such controlchamber including means for closing or opening a vent in the uppermostregion of the siphon conduit, dependent on the presence or absence ofliquid, e.g. water, in the hydrostatic column at a level correspondingto a desired pressure in the classifier, which pressure cor-responds, inturn, to a desired accumulation of solids in the hindered settlingcolumn.

An effective and simple control arrangement in the stated chambercomprises a float carrying a needle or cone-type valve element which maybe raised by the float to close a tube leading to the siphon vent. Thuswhen -a pulp of accumulating solids of sufficient density is reached andmaintained, say at the foot of the hinderedsettling column where thesiphon opens, the increased pressure caused by such solids in acondition of so-called teeter raises the water in the hydrostatic column(which is essentially clear water, since there is no upward flow tocarry solids) to a significantly high level, above the overflow level ofthe classifier. Under such circumstances, i.e. when a level of selectedheight is reached, the valve closes and siphon action is thereuponinitiated, conducting a pulp or slurry of the desired, classified solidparticles to the point of discharge. If insuflicient solid particles areaccumulating, or solid particles of insufficient size (or settlingrate), the pressure in the solids-containing body of water at the footof the settling column falls, thereby lowering the level in thehydrostatic column. In consequence the float descends, opening the ventof the siphon and interrupting its discharge action.

Product discharge arrangements of the above character are more fullydescribed in the cited patent, further instances of utilization of suchsiphon discharge means being shown with other hydraulic classifiersembodying hindered settling columns, i.e. in US. Patent No. 2,784,841granted March 12, 1957 on the application of the present applicant, andlikewise in US. Patent No. 2,967,167, granted January 10, 1961 and U.S.Patent No. 3,032,194 granted May 1, 1962, on applications of the presentapplicant and Harvie W. Breathitt, Jr. A still further arrangement ofsuch siphon discharge control is disclosed and claimed 3,280,975Patented Oct. 25, 1966 in the copending application of the presentapplicant and Harvie W. Breathitt, Jr., Serial No. 111,320, filed May19, 1961, where the control chamber includes electrode means sensitiveto the level of water in the hydrostatic pipe, with arrangementsgoverned thereby for opening and closing the vent in the siphon.

Whereas the foregoing devices have been found to function veryeifective'ly, with remarkable control of the nature of the productdischarge, i.e. as to its limitation to desired characteristics of size(or more generically, settling rate) in such product, experience hasindicated that with relatively light weight minerals or similarsubstances the actual elevation, or more accurately, the superelevationof the liquid in the hydrostatic column may sometimes be inconvenientlylow. No difiiculty has, in general, been encountered with substancessuch as phosphate rock, sand, and a variety of heavier minerals, but inthe case of materials such as coal or equivalent solids having aspecific gravity of not more than about 2.0, the valve control chamber(which may be adjusted in vertical position) may have to be located tooclose to the overflow level of the classifier, for convenience ofoperation, adjustment or servicing, and indeed for optimum, positivecontrol of the siphon action. That is to say, if hindered settlingclassification is applied to particles of coal or similar material, e.g.having a specific gravity of not more than 1.2 to 1.5, the accumulationof such solids in teeter, as at the lower region of the classifiercolumn, does not increase the pressure (above that of the normal head ofwater) by anything like as large an amount as occurs with phosphaterock, sand or heavier substances. Thus even under optimum conditions ofproduct accumulation, the increase in density of the pulp in thesettling column at the locality of product Withdrawal is relativelysmall, and the float box or equivalent chamber must then be situatedunduly close to the overflow level of the classifier, for convenience ofobservation, servicing and use.

In accordance with the present invention, means and methods of operationare provided whereby an amplified or exaggerated level ofsuper-elevation is achieved in the hydrostatic column, so that thecontrol chamber may be situated at a correspondingly higher position,well above the top of the siphon. In this locality of greater elevation,the control instrumentalities are much more conveniently located andserve more positively and reliably for the desired function of governingthe siphon discharge. In consequence the system functions in athoroughly satisfactory manner, with proper regulation of the withdrawalof product particles, unaffected by the fact that such mineral may be ofrelatively low specific gravity.

Specifically, the method of the invention embraces supplying to thehydrostatic column a flow of water under considerable head, i.e. aconstant pressure, of a suitable, selected value. That is to say,although the pipe extending from the control chamber to the locality ofaccumulating solids in teeter may conveniently be denoted as ahydrostatic column, a considerable part of its length is now traversed(i.e. according to the invention) by a continuous flow of water underthe additional, constant pressure. The portion of the column whichextends above the locality of introduction of water flow, then providesa control level (i.e. the liquid rises to such level) which is governed,in eifect, by the sum of the pressure of flowing water supply and thepressure contributed by the collecting solids. As explained above, thepressure in the hindered settling column is normally increased inaccordance with the increase of apparent density of the solids-liquidsuspension in teeter.

Hence, an example of effective embodiment of the invention embraces thesupply of the hydrostatic column, ad-

vantageously at a region slightly above the tank overflow level, ofwater under a constant pressure. In order for this water to be drivendownward through the hydrostatic column connection and out at the regionat the foot of such column, there must be sufiicient head to effectu atesuch flow out of the bottom opening of the hydrostatic column. Thecontrol point of level of water, e.g. clear water in the hydrostaticpipe, is thereby substantially raised above its otherwise normallocality. In all other respects the discharge-controlling function andoperation are the same. With the control chamber or box located at anamplified super-elevation, operation proceeds as would be achieved (e.g.with substantially heavier minerals) with heavier feed. The controlchamber is thus set at a correspondingly higher locality, i.e. as neededfor the defined siphon control function.

Stated in another way, the control column portion (of the hydrostaticpipe) which extends above the point of entry of the supplemental watersupply, constitutes a true hydrostatic column, where the liquid levelfor desired siphon action is greatly raised above the point where itwould otherwise be placed. Although, as will be understood, otherarrangements for supplying a flow of water at a constant pressure may beemployed, an effective arrangement involves what might be described as aconstant head water tank connected by a suitable pipe to the hydrostaticcolumn or pipe (e.g. at the aforementioned locality) for example betweenthe classifier overflow level and the point of normal super-elevation.With liquid flowing on downward through the control pipe into thehindered settling column, say at the foot thereof, the supplementalpressure of such flowing liquid (i.e. the pressure causing its flow)causes exaggerated or amplified super-elevation of water level in thehydrostatic pipe, so as to enable disposition of the control chamber orfloat box at the conveniently higher level.

In other words, the float box or its equivalent is then set at asubstantially higher point, i.e. to control the siphon for initiation ofdischarge when desired accumulation of particles in teeter is reached atthe bottom or other withdrawal locality of the hindered settling column.In other respects, the system functions as in previous embodiments, e.g.as in the cited patents. When pressure occasioned by the increaseddensity of the solids-containing liquid reaches a desired point, thelevel in the hydrostatic column (now at an amplified place ofsuper-elevation) effectuates closure of the vent in the siphon. Thesiphon, which heretofore had a tendency only to carry across clearliquid (in spurts or surges, as explained in the cited patents) nowconstitutes a functioning siphon and provides a discharge of the desiredpulp of classified particles. That is to say, the pressure of liquid atthe foot, filling the siphon first with clear water, promptlyeffectuates continuance of flow into the siphon, carrying particles ofsolid with it. The vent being closed, there is true siphon action,whereas with the vent open, the pressure at the foot is insuificient tocarry the pulp as such above the tank overflow level.

It will be understood that the exaggerated condition in the hydrostaticcolumn is directed solely to that column, the action of the siphon beingdependent only on the condition of liquid and solids in the hinderedsettling column itself. Providing the uppermost turn of the siphon isabove the tank overflow level, there is nevertheless efi'ective controlof the siphon by opening and closing the vent, with the furtherprovision that such uppermost part will be disposed below the level ofnormal or ordinary super-elevation in the hydrostatic column, i.e. thelevel that would be reached under desired conditions without the meansand procedure of the present invention.

By way of simple further explanation of the function of the meansproviding exaggerated super-elevation, it might be stated that if thehydraulic classifier is filled only with water and water is thenintroduced into the hydrostatic pipe, there will be a flow into theclassifier through such pipe. As the flow of water begins and isincreased, the water in the hydrostatic pipe (e.g. in the upper portionthereof extending above the point of introduction of water) will rise sothat for each rate of flow it reaches and maintains a correspondinglevel which represents sufficient head to force the water (flowing atthe attained rate) through the lower part of the pipe and out into theclassifier. As feed of solids is thereafter introduced into [theapparatus, and the classifying function, including establishment of ateeter column or hindered settling column, comes into play, theaccumulating density of pulp at the foot of the hydrostatic pipe resultsin additional build-up of head in the clear water in the pipe; this headdue'to hindered settling operation, being represented by furtherelevation of the level in the upper portion of the pipe, is as requiredin order to continue the downward flow of water through such pipe.

Thus for any given rate of water flow, as may be determined by settingof an appropriate valve, the superelevation or head (as last mentioned)corresponding to the increase of fluid density at the foot of thehydrostatic pipe is superimposed on the supplemental head or pressurenecessary to force the water down and through. This supplemental oradded head, occasioned by the flow of water under pressure to andthrough the hydrostatic pipe, produces an amplification of the operatingsuper-elevation in the hydrostatic pipe, and thus provides thecorrespondingly higher locality for the control instrumentalities, inaccordance with the present invention.

As will now be seen, the adjustment of a valve or other instrumentalityfor controlling the water flow provides a mode of adjusting the extentof super-elevation, the liquid upstream of such valve beingadvantageously supplied at a constant pressure. Indeed it will beunderstood that at any given setting of the valve, there will not onlybe a definite corresponding rate of water flow (because the pressureupstream of the valve is constant) but there will also be acorrespondingly definite, and somewhat lower pressure immediatelydownstream of the valve, i.e. as occasioned by the drop across theorifice which the valve provides. Thus the last-mentioned pressure, atthe downstream of the valve, in effect represents the extent ofamplification of the super-elevation expected in the hy drostatic pipe.In other words, the valve adjustment determines the rate of flow of thesupplied liquid and correspondingly determines, in accordance with theadjusted pressure at the downstream side of the valve, the amount bywhich the liquid level in the hydrostatic pipe is raised above thenormal super-elevation which is imparted to it because of accumulatingsolids in teeter in the hindered settling column.

Further features and advantages of the invention will be apparent fromthe detailed description hereinbelow set forth, together with theaccompanying drawing, which illustrates in schematic elevational view(partly in vertical section) a hydraulic classification systemincorporating the apparatus of the present invention in an exem plifyingembodiment.

There is shown in the drawing a hydraulic classifier of thehindered-settling type, represented by a tank 10 comprising an uprightcylindrical tank section 11 opening downward into a wider cylindricaltank section or pocket 12. Means are provided for the continuousintroduction of water in considerable quantity to a lower region of thispocket, e.g. a valved pipe 14 opening horizontally into the side wall ofthe pocket. Immediately above the locality of introduction of Water is aso-called constriction plate 17 separating the lower region 18 of thepocket from the upper region thereof; this plate has multipleperforations of suitable size, through which the water introduced by thepipe 14 flows with considerable velocity to rise in the column 11 andprovide hinderedsettling conditions therein. For purposes of drainage atdesired times, a valve pipe (normally closed) extends downwardly fromthe lower end of the pocket 12.

The classifier structure also includes a feed pipe 22, shown as openinginto the upper portion of the tank section 11 at one side. Through thispipe, divided solid materials to be classified are advanced in the formof a pulp mixed with water. In addition, an annular launder 23concentrically surrounds the upper extremity of the tank section 11 toreceive overflow from the tank. The overflow is removed from the launderas through a downwardly extending outlet pipe 24.

In operation, the tank 10 is maintained filled with water by continuoussupply of the aqueous pulp through the feed pipe 22 and continuous flowof so-called hydraulic water to the tank through the pipe 14. The solidsto be classified, introduced in the pulp to the tank section 11, tend tosettle downwardly through the tank. However, the upward flow of waterfrom the pipe 14, as augmented in velocity by passage through theconstriction plate 17, inhibits the settling of solids and creates inthe tank section 1.1 a hindered-settling column wherein solid particlesare maintained in a condition of suspension or teeter. Consequently,primarily only the largest or fastest-settling of the introducedparticles can reach the pocket 12 in the lower portion of the tank,while the particles of slowest settling rate, e.'g. fines, are carriedupwardly through the section '11 and away from the tank with theoverflow to the launder 23. In other words, such hindered-settlingoperation separates the introduced solid particles according to settlingrate, and provides in the pocket 12 an accumulating suspension ofparticles which are primarily of the largest or fastest-settlingfraction, -i.e. that fraction of the introduced particles which it isordinarily desired to separate and recover.

The apparatus of the present invention in the form shown is adapted toeffect the controlled discharge of this classified product from thepocket 12 as an aqueous pulp containing particles chiefly of the desiredlarge size or tast settling rate, and includes a siphon conduit systemof the type disclosed in the aforementioned U.S. Patent No. 2,714,95 8.Thus there is provided an enlarged lower conduit section 25 openingdownwardly into the pocket 12 and connected at its upper end with a longpipe section 26, of smaller diameter, extending upwardly to a localityabove the tank overflow level. At this latter locality the pipe section26 communicates as through a T-fit'ting chamber 28 with a further pipesection 29, which extends horizontally beyond the tank and thencedownwardly' to a suitable external discharge location (not shown) at anelevation lower than the liquid level in the tank. To assist the siphonaction, and in particular to facilitate its initiation or resumption, asupplemental flow of water is introduced to the lower section 25 asthrough a valved priming pipe 30. Desirably the pipe section 26 extendsdownwardly through the upper portion of the section 25 to open thereinat a level lower than the opening of the printing pipe 30, asillustrated.

The discharge structure fiunther includes a pipe section 31, providing ahydrostatic column, opening downwardly in the pocket 12 at about thelevel of the opening of the siphon section '25 and extending upward fora considerable distance above the liquid level in the tank 10. Thishydrostatic pipe 31 communicates through a section of flexible tubing 33with a float valve chamber 34, shown as carried by a bracket which ismounted on the upper extension of the pipe 31 and is adjustable to varythe vertical position of the chamber 34 as desired. The latter chamberis positioned a predetermined distance above the tank [[0 and above theT-fitting chamber 28 of the siphon conduit system. At its top, thischamber 34 communicates with the atmosphere through a vent 37, and alsowith a flexible air vent tube 38 which opens into the siphon conduitsystem 25-29 at the T-fitting chamber 28. Within the chamber 34 is aneedle valve float element which is adapted, on floating upward, toclose the air vent tube 38.

As previously explained, the establishment of a condition of teeter inand above the pocket 12 increases the fluid pressure in the pocket to avalue greater than normal liquid pressure at that region by an amountdirectly related to the density and size or settling rate of particlesin teeter therein, with the result that water rises in the hydrostaticpipe '31 to a level of super-elevation, i.e. above the overflow level ofthe tank 10, representative of such increased pressure. The float valvechamber is positioned for closure of the air vent tube 38 by the element40 when a predetermined increased pressure corresponding to a desiredaccumulation of solids in teeter is attained in the pocket 12, i.e. anincreased pressure effective to raise water in the hydrostatic pipe to apredetermined level of super-elevation. The T-fitting chamber 28 of thesiphon conduit system is located below the latter level.

With this arrangement of elements, product discharge through the siphonsystem can occur only if the pressure in the pocket is at or above theaforementioned predetermined value. When this pressure is less than suchvalue, the float valve is open and hence the T fitting chamber 28 of thesiphon system communicates with the atmosphere through the tube 38,preventing regular siphon action or withdrawal of product pulp from thepocket 12, although some water may pass through the siphon in spurts orsurges. When the pressure in the pocket is at or above the selectedminimum value, however, the element 40 of the float valve is buoyed upto close the tube 38, sealing the siphon system from the atmosphere andthereby enabling the development of a continuous, eflective siphonaction in the system 254.9 to provide steady delivery of the classifiedproduct from the pocket. In other Words, the hydrostatic pipefloa'tvalve control regulates the functioning of the siphon system withrespect to pressure in the pocket, permitting siphon action to occuronly while a desired accumulation of solids in teeter (as represented bysuch pressure) is maintained in the pocket, to insure delivery of only aproperly classified product pulp through the siphon.

According to prior practice, for such control the float valve chamber 34would be disposed at the normal level of super-elevation to which waterrises in the hydrostatic pipe when the desired pressure is attained inthe pocket, so that such super-elevation of Water, communicated to thefloat valve chamber 34 by the tubing 33, will buoy up the element 40 toclose the air vent tube 38. As further noted above, however, in theclassification of mineral or other "solids (such as coal) having aspecific gravity not more than about 2.0, the latter normal level evenunder optimum hindered-settling conditions is inconveniently colse tothe overflow level of the tank 10. To obviate this difiiculty, and inparticular to enable the positioning of the chamber 34 at anadvantageously greater elevation relative to the tank overflow, theapparatus of the present invention in its illustrated form includes, incombination with the above-described elements of the siphon dischargeand control system, structure for exaggerating or artificially raisingthis level of super-elevation to a substantially greater height abovethe tank.

This latter structure is specifically arranged to supply to thehydrostatic pipe 31 a continuous flow of water at a predeterminedconstant pressure, delivered through a horizontal conduit 42 (desirablyof approximately the same diameter as the pipe 31) which communicateswith the pipe 31 at a suitable locality below the level at which it isdesired to position the float valve chamber 34, and convenientlyslightly above the overflow level of the tank 10. As shown, thestructure further includes a tank 43 disposed above the horizontalconduit 42 and surrounded at its upper extremity by an annularoverflow-collecting launder 44 having a suitable drain outlet 45. Thistank is maintained entirely filled with water supplied in continuousflow, eg through a conduit 47 opening downwardly above the tank 43 andcontrolled by a valve 49. At the lower end of the tank 43 adownwardly-tapering tank outlet funnel 50 communicates with a verticalpipe section 51 (also desirably of about the same diameter as the pipe31) extending downward to and connecting with the horizontal conduit 42.A control valve 53 is connected in the pipe section 51. In addition, theconduit 42 may conveniently be connected to the conduit 47 at a pointupstream of the valve 49 through a further pipe section 56 controlled bya normally closed valve 58, and the upper end of the funnel 50 may becovered with a screen 60 to prevent clogging of the narrow portion ofthe funnel or the pipe 51, e.g. by foreign matter.

In operation, with the valve 58 closed and the valve 49 open, the flowof water introduced by the conduit 47 flows through the tank 43 and pipe51 to the horizontal conduit 42, and thence to the hydrostatic pipe 31.The tank 43 serves to provide a constant head of water at the valve 53,so that by appropriate setting of the latter valve to provide a givenconstant pressure drop across the valve, the water flowing to thehydrostatic pipe through the conduit 42 will be at a constant pressure,i.e. determined by the vertical distance between the overflow level ofthe tank 43 and the conduit 42, and the pressure drop across the valve53.

Assuming that the tank 10 is filled with water only, so that there is nocondition of hindered settling therein, this constant-pressure flow fromthe conduit 42 into the hydrostatic pipe 31 will continuously flowdownward through and out of the latter pipe upon the development of asuificient head of water 'in the hydrostatic pipe. Accordingly, waterrises in the hydrostatic pipe to a level, above the overflow level ofthe tank 10, representative of such head. The extent of elevation ofthis level (herein termed the control level) is dependent upon thepressure of the water introduced through the conduit 42, and the controllevel can therefore be readily positioned at a desired elevation byappropriate setting of the valve 53 which determines the pressure of theintroduced water.

When a condition of teeter is established in and above the pocket 12,the resultant increase of pressure at the latter region requiresdevelopment of a greater head in the hydrostatic pipe 31 to force theflow of introduced water from the conduit 42 down through and out of thepipe. Accordingly, water rises in the hydrostatic pipe, to provide suchgreater head, until it reaches a level which is higher than theaforementioned control level by an amount equal to the normal extent ofsuper-elevation which the condition of teeter would otherwise produce inthe hydrostatic pipe (i.e. in the absence of the supplemental flow fromthe conduit 42). In other words, with the constant-pressure flow fromthe conduit 42 supplied to the pipe 31, any given accumulation of solidsin teeter in the tank 10 will raise the water in the pipe 31 to a levelof super-elevation which is exaggerated, or raised above the normallevel of super-elevation resulting from such accumulation, by thevertical distance of the control (or non-teeter) level above theoverflow level of the tank 10. Thus, referring to the drawing, if thelevel 62 represents the normal extent of super-elevation for a givenaccumulation of solids at which it is desired to initiate siphon actionby closure of the float valve, and the level 63 represents theexaggerated level of super-elevation produced by the supplemental flowfrom the conduit 42 (for the same accumulation of solids in the pocket12), the distance between the levels 62, 63, i.e. the extent ofexaggeration or raising of the level of super-elevation, is equal to theheight of the control level (line 65) above the overflow level 64 of thetank 10.

As will therefore be appreciated, the continuous flow of water atconstant pressure from the conduit 42 serves to raise the level ofsuper-elevation by an amount which is dependent on the pressure of thisflow and which can accordingly be fixed at a desired value byappropriate setting of the valve 53. With the degree of super-elevationin the hydrostatic pipe thus enhanced, the float valve chamber 34 ispositioned above the normal level of superelevation at which it mustotherwise be placed; specifically, and as illustrated in the drawing,its location is elevated above such normal level by a distance equal tothe height of the control level above the tank overflow. As previouslymentioned, this higher position of the float valve has particularlyimportant advantages, from the standpoint of effective operation andconvenience, in the classification of low-density solids or in othersituations wherein the normal extent of super-elevation is of smallmagnitude.

In all other respects, the discharge of product pulp with the dischargesystem incorporating the foregoing structure for exaggerating the extentof super-elevation is essentially the same as that of the dischargesystem disclosed in the aforementioned US. Patent No. 2,714,958. Thus,the variations in the amount of super-elevation produced in thehydrostatic pipe 31 by variations in the accumulation of solids in thepocket 12 are of the same magnitude as if the supplemental flow to thepipe were not provided, but these variations occur at a higher levelrelative to the overflow level of the tank 10. The siphon action isentirely unaffected, the T-fitting chamber 28 being positioned (asbefore) below the normal level of super-elevation 62. Siphon action, anddelivery of product from the pocket 12, can occur only when theexaggerated level of super-elevation in the pipe 31 is at or above :apredetermined level in the float valve chamber 34 (i.e. a levelrepresentative of a desired accumulation of solids in the pocket) sothat the element 40 is buoyed up to seal the tube 38 from theatmosphere.

It will accordingly be understood that the product discharge method ofthe present invention, as performed with the described and illustratedapparatus, involves withdrawing product pulp from the pocket 12 bysiphon action (viz. through the conduit system 25-29) under control of ahydrostatic column (i.e. in the pipe 31), and supplying to the lattercolumn a continuous flow of water at constant pressure for raising thelevel of super-elevation therein by a constant amount; this columnoperates as through the float valve structure 34-40 to permit suchsiphon action to occur only when a predetermined accumulation of solids,as represented by a particular level of super-elevation, is maintainedin the pocket.

For clarity of illustration the structure and operation of the apparatusare shown in the drawing in a schematic manner (rather than with precisedimensional accuracy) and indeed as functioning with a ratherconsiderable addition to the head .in the hydrostatic pipe; the valve 53may of course be adjusted to provide any desired (greater or less)exaggeration of the super-elevation, e.g. as by reducing the flow in thepipe 42 to bring the non-teeter head point (line 65) closer down towardthe classifier overflow level 64 if less amplification in thehydrostatic pipe will suflice. For instance, in one system, where theopening of the funnel 50 was 10 /2 inches below the constant level ofwater in the tank 43 and inches above the horizontal pipe 42, the valve53 was readily settable for a range of super-elevations (line 65) in thepipe 31, one instance of satisfactory operation providing a height ofthe level 65 of 12 inches above the classifier level 64,

to afford convenient further elevation of the hindered settling controllevel 63 as shown. In this example, the portion of the hydrostatic pipe31 extending below the classifier level 64 had a diameter of 1 /2inches, and the supplemental flow to this pipe from the horizontal pipe42 was supplied at a flow rate of 5 gallons per minute. An equivalentextent of exaggeration of super-elevation can be attained with lowerflow rates (i.e. a smaller supplemental flow) if the diameter of thehydrostatic pipe 31 is reduced.

Although in the drawing the extent of exaggeration of super-elevationshown is such that the horizontal pipe 42 enters the hydrostatic pipe 31below the control level 65,

it will be appreciated that the pipe 42 can enter the pipe 31 at ahigher point, i.e. above the latter control level.

It may further be noted that the structure illustrated may if desired beemployed to effect the ordinary controlled discharge of product from thepocket 12 in the manner disclosed in the last-cited patent, i.e. withoutexaggerating the level of super-elevation, for the classification ofhigher-density solids as to which the normal level of super-elevationmight approximate the level 63. This is accomplished simply by closingthe valves 49, 53 in addition to the valve 58 so that there is no flowof water through the conduit 42 to the pipe 31 and hence no exaggerationof the level of super-elevation in the latter.

Again the supplemental fiow through the conduit 42 may be used to clearthe hydrostatic pipe 31, e.g. when operation of the hydraulic classifieris resumed after an interruption which has left a settled deposit or bedof particles at the lower end of the hindered-settling colum. Sometimes,upon such resumption, the initial flow of hydraulic water from the pipe14 may (due to back pressure created by the deposit of particles)temporarily have suflicient force to carry particles upward into thehydrostatic pipe, clogging it. By closing the valves 49 and 53, openingthe valve 58, and directing through the then-connecting conduit 56, 42to the pipe 31 a highpressure flow of Water from the source supplyingthe conduit 47, such particles can be elfectively dislodged. To preventupward diversion of this high-pressure flow in the pipe 31, a valve 66(normally open, but closed for such clearing operation) may be connectedin the pipe 31 intermediate the level of the conduit 42 and the floatvalve chamber 34.

As will be appreciated, the method of the present invention may bepracticed using other means for supply of a constant-pressure flow ofwater to the hydrostatic column, i.e. means alternative to the constanthead tankcontrol valve arrangement illustrated. Moreover, while theprocedures and apparatus of the present invention have been shown anddescribed as used with a simplified form of hydraulic classifier, thesame may be employed for provision of product discharge from other typesof hindered-settling classifiers, and to deliver classified fractions ofparticulate material other tthan the fraction constituting thefastest-selling particles, to which reference has herein been made. Inaddition, the invention is of course adapted for use not only inconnection with the classification of low-density solids, but also inother situations wherein hindered settling classification operation mayproduce an inconveniently slight pressure increase (represen-ted by alow level of super-elevation) at the locality from which discharge is tobe effected.

It is to be understood that the present invention is not limited to thespecific features and embodiments herein shown and set forth, but may becarried out in other ways without departure from its spirit.

I claim:

1. In the hydraulic classification of solid particles by hinderedsettling in a liquid filled classifier column wherein accumulatingsolids of desired character for separation create a liquid-solidsmixture having an increased density relative to the liquid alone, in theclassifier column at a predetermined region of such accumulation, themethod of Withdrawing a pulp of said accumulating solids from saidregion which comprises establishing a hydrostatic column of liquidextending upwardly from said region, supplying additional liquid to anupper locality of said hydrostatic column under constant pressure forcontinuous flow of said liquid down the hydrostatic column into theliquid body in the classifier column, said increased density at saidregion being eflective to elevate liquid in the hydrostatic column to acorresponding distance above the upper level of liquid in the classifiercolumn and said supply of water into the hydrostatic column beingeffective to provide additional elevation of said liquid in thehydrostatic column to a predetermined control region, and initiating andcontrolling discharge of pulp from said first-mentioned region ofaccumulation of solids in accordance with presence and absence,respectively, of liquid in the hydrostatic column at a predeterminedlevel in said last-mentioned control region.

2. In the hydraulic classification of solid particles by hinderedsettling in a liquid filled classifier column where in accumulatingsolids of desired character for separation create a liquid-solidsmixture having an increased density relative to the liquid alone, in theclassifier column at a predetermined region of such accumulation, themethod of withdrawing a pulp of said accumulating solids from saidregion by flow through a siphon extending from the region to and downfrom a locality above the upper level of liquid in said classifiercolumn, which comprises establishing a hydrostatic column of liquidextending upwardly from said region, supplying additional liquid to saidhydrostatic column under constant pressure for continuous flow of saidliquid down the hydrostatic column into the liquid body in theclassifier column, said increased density at said region being effectiveto elevate liquid in the hydrostatic column to a level of normalsuper-elevation spaced a corresponding distance above the aforesaidlevel of liquid in the classifier column and said supply of water intothe hydrostatic column being effective to provide additional elevationof said liquid in the hydrostatic column to a predetermined controlregion, and initiating and controlling discharge of pulp through thesiphon in accordance with presence and absence, respectively, of liquidin the hydrostatic column at a predetermined level in saidlast-mentioned control region, said locality to which said siphonextends being lower than a pre-selected level of normal superelevationin said hydrostatic column corresponding to a predetermined accumlationof solids in said first mentioned region in said classifier column.

3. A method according to claim 2, wherein said additional liquid issupplied to said hydrostatic column at a locality of said hydrostaticcolumn above said upper level of liquid in said classifier column andbelow said control region.

4. A method according to claim 3, wherein said step of supplyingadditional liquid to said hydrostatic column comprises establishingabove the level of said last-mentioned locality of said hydrostaticcolumn a liquid-filled constant head region providing a predeterminedconstant head of liquid above said locality, and continuously conductingliquid from said constant head region to said hydrostatic column at saidlocality While decreasing the pressure of said liquid by a predeterminedconstant amount and while continuously supplying liquid to said constanthead region to maintain said region filled with liquid as aforesaid.

5. In a hydraulic classifier, in combination, means providing a hinderedsettling column, including means supplying solid particles thereto forclassification ac- .cording to settling rate and means supplyinghydraulic liquid for efi ectuation of hindered settling, to produce apredetermined accumulation of solid particles having desiredcharacteristics of settling rate, in teeter at a predetermined region ofsaid column, said classifier including structure providing an upperlevel of liquid in the classifier, means for withdrawing pulp ofaccumulating solids from said region for discharge of said particles asproduct, a hydrostatic pipe opening into the column at said region andextending above the aforesaid liquid level of the classifier, wherebyliquid from the column is caused to rise in said hydrostatic pipe abovesaid level by reason of increased pressure occasioned by the aforesaidaccumulating particles in teeter, means for supplying a supplementalflow of liquid into said hydrostatic pipe at a substantially constantpressure, said means being connected to said pipe to direct said flowtherein at an intermediate locality thereof and being effective tocreate additional liquid-elevating pressure in the hydrostatic pipe,said hydrostatic pipe including a portion extending above the localityof said connection of the liquid supplying means, and means associatedwith said last-mentioned portion of the hydrostatic pipe at a localityspace above the aforesaid liquid level of the classifier by a distancecorresponding to the elevation of liquid due both to the pressure ofsolids in teeter and the aforesaid additional pressure, for controllingflow of pulp through the aforesaid discharge means to maintain said flowof pulp when the accumulating solids in teeter produce pressurecorresponding to the predetermined accumulation of solids having desiredcharacteristics of settling rate.

6. In a hydraulic classifier, in combination, means providing a hinderedsettling column, including means supplying solid particles thereto forclassification according to settling rate and means supplying hydraulicliquid for etfectuation of hindered settling, to produce a predeterminedaccumulation of solid particles havling desired characteristics ofsettling rate, in teeter at a predetermined region of said column, saidclassifier including structure providing an upper level of liquid in theclassifier, siphon means for conducting pulp of accumulating solids fromsaid region up to and down from a locality above said las-t mentionedliquid level, for discharge of said particles as product; a hydrostaticpipe opening into the column at said region and extending above theaforesaid liquid level of the classifier, whereby liquid from the columnis caused to rise in said hydrostatic pipe above said level by reason ofincreased pressure occasioned by the aforesaid accumulating particles inteeter, to a level of normal super-elevation spaced above said upperlevel of liquid by a distance corresponding to said increased pressuremeans for supplying a supplemental flow of liquid into said hydrostaticpipe at a substantially constant pressure, said means being connected tosaid pipe to direct said flow therein at an intermediate localitythereof and being effective to create additional liquid-elevatingpressure in the hydrostatic pipe, said hydrostatic pipe including aportion extending above the locality of said connection of the liquidsupplying means, and means associated with said last-mentioned portionof the hydrostatic pipe at a control locality spaced above the aforesaidliquid level of the classifier by a distance corresponding to theelevation of liquid due both to the pressure of solids in teeter and thethrough said siphon means to maintain said flow when the accumulatingsolids in teeter produce pressure corresponding to the predeterminedaccumulation of solids having desired characteristics of settling ratesaid locality up to and down from which said siphon means conducts saidpulp being lower than a preselected level of normal super-elevation insaid hydrostatic pipe corresponding to said predetermined accumulationof solids.

7. Apparatus as defined in claim 6, wherein said siphon means includes avent at a locality above the said level of liquid in the classifier andwherein the control means in the hydrostatic pipe comprises a controlchamber and liquid level responsive means therein for closing andopening said vent in accordance respectively with presence or absence"of liquid at said control locality in the hydrostatic pipe.

8. Apparatus as defined in claim 6, which includes constant-pressureliquid supply means connected to said means for supplying liquid intothe hydrostatic pipe, and valve means intermediate saidconstant-pressure means and said means for supplying liquid into thepipe, for adjusting the rate of flow of said liquid and for therebyadjusting the extent to which liquid is elevated in the aforesaidportion of the hydrostatic pipe by reason of said supplemental liquidsupply, the aforesaid connection of the liquid supplying means with thehydrostatic pipe being disposed at a locality of said pipe above thelevel of liquid in the classifier.

9. Apparatus as defined in claim 8, wherein said con-,

References Cited by the Examiner UNITED STATES PATENTS 8/1955 Evans209-158 8/1955 Fit-ch 209-496 X FRANK W; LUTTER, Primary Examiner.

1. IN THE HYDRAULIC CLASSIFICATION OF SOLID PARTICLES BY HINDEREDSETTLING IN A LIQUID FILLED CLASSIFIER COLUMN WHEREIN ACCUMULATINGSOLIDS OF DESIRED CHARACTER FOR SEPARATION CREATE A LIQUID-SOLIDSMIXTURE HAVING AN INCREASED DENSITY RELATIVE TO THE LIQUID ALONE, IN THECLASSIFIER COLUMN AT A PREDETERMINED REGION OF SUCH ACCUMULATION, THEMETHOD OF WITHDRAWING A PULP OF SAID ACCUMULATING SOLIDS FROM SAIDREGION WHICH COMPRISES ESTABLISHING A HYDROSTATIC COLUMN OF LIQUIDEXTENDIG UPWARDLY FROM SAID REGION, SUPPLYING ADDITIONAL LIQUID TO ANUPPER LOCALITY OF SAID HYDROSTATIC COLUMN UNDER CONSTANT PRESSURE FORCONTINUOUS FLOW OF SAID LIQUID DOWN THE HYDROSTATIC COLUMN INTO THELIQUID BODY IN THE CLASSIFIER COLUMN, SAID INCREASED DENSITY AT SAIDREGION BEING EFFECTIVE TO ELEVATE LIQUID IN THE HYDROSTATIC COLUMN TO ACORRESPONDING DISTANCE ABOVE THE UPPER LEVEL OF LIQUID IN THE CLASSIFIERCOLUMN AND SAID SUPPLY OF WATER INTO THE HYDROSTATIC COLUMN BEINGEFFECTIVE TO PROVIDE ADDITIONAL ELEVATION OF SAID LIQUID IN THEHYDROSTATIC COLUMN TO A PREDETERMINED CONTROL REGION, AND INITIATING ANDCONTROLLING DISCHARGE OF PULP FROM SAID FIRST-MENTIONED REGION OFACCUMULATION OF SOLIDS IN ACCORDANCE WITH PRESENCE AND ABSENCE,RESPECTIVELY, OF LIQUID IN THE HYDROSTATIC COLUMN AT A PREDETERMINEDLEVEL IN SAID LAST-MENTIONED CONTROL REGION.